On Sunday evening, my eyes were glued to eight windows on my computer screen, watching data pop up every few seconds. NASA’s Cassini spacecraft was making its lowest swing through the atmosphere of Saturn’s moon Titan and I was on the edge of my seat. Trina Ray, a Titan orbiter science team co-chair, was keeping me company. Five other members of my team were also at JPL. Between us, we were keeping an eye on about 2,000 data channels.

One of the 34-meter antennas at the Deep Space Network’s Goldstone complex, DSS-24, was pointed at Saturn and listening for the signal that was expected to be here in just a few minutes. The data would be arriving at my computer as quickly as they could be sent back to Earth, though there was an agonizing hour-and-18-minute delay because of the distance the data had to travel. (We call this flyby T70, but it is actually Cassini’s 71st flyby of Titan.)

It was a nervous time for me — the previous night we had been at JPL to send some other real-time commands to the spacecraft when an alarm came in indicating that the magnetometer, the prime instrument taking data for the T70 flyby, needed a reset. Fortunately, the controller on duty immediately called the magnetometer instrument operations team lead in England. Within 90 minutes, the commands were on their way to do a computer reset and clear the alarm. At 2 a.m. Pacific time on Sunday, we got the email indicating all was well and the magnetometer was ready for the Titan closest approach.

So here we were, past one hurdle, hoping nothing else would come up. We had run hundreds of simulations over the past three-and-a-half years, so I knew we had done everything we could think to do. We did more training for this event than anything else we had done since we dropped off the Huygens probe in January 2005 for a descent through the moon’s hazy atmosphere.

Right on time, at 7:26 p.m., the Deep Space Network locked on the spacecraft downlink, a good start. I was focused on the data for spacecraft pointing. As long as we stayed within an eighth of a degree of the expected pointing, everything would be fine. At 7:45 p.m., we got the data from closest approach, a mere 880 kilometers (547 miles) in altitude. Over the vocabox, a cross between a telephone and walkie-talkie, the attitude control team reported that the thrusters were firing about twice as much as we expected. The Titan atmosphere appeared to be a little thicker than we expected, even though we had fed about 40 previous low Titan flybys by Cassini and the descent data from Huygens into our modeling.

But spacecraft control was right on the money, keeping the pointing within our predicted limits. Even with the extra thrusting, we stayed well within our safety margin.

At 7:53 p.m., the spacecraft turned away to go to the next observation. I let out a sigh of relief, happy that everything during closest approach had gone just as we planned. Five attitude control guys crowded into my office with smiles on their faces. Trina and I were marveling at what a wonderful spacecraft we have to work with. Another first for the Cassini mission!

Now, as Trina says, we have to finish the job by returning all the great science data. We have data playbacks today at two different Deep Space Network stations to make sure we have – as we say here – both belts and suspenders. Engineers will also go back to analyze the data with the scientists to see just how dense the Titan atmosphere turned out to be at our flyby altitude.

But last night, at least, my team and I went home happy!

Julie Webster, spacecraft operations team manager for NASA’s Cassini spacecraft, oversees the engineering subsystems and overall spacecraft health and safety. She is a systems engineer at JPL.

This weekend, Cassini will embark on an exciting mission: trying to establish if Titan, Saturn’slargest moon, possesses a magnetic field of its own. This is important for understanding the moon’sinterior and geochemical evolution.

For Titan scientists, this is one of the most anticipatedflybys of the whole mission. We want to get as close to the surface with our magnetometer as possible fora one-of-a-kind scan of the moon. Magnetometer team scientists (including me) have a reputation forpushing the lower limits. In a world of infinite possibilities, we would have liked many flybys at 800kilometers. But we went back and forth a lot with the engineers, who have to ensure the safety of thespacecraft and fuel reserves. We agreed on one flyby at 880 kilometers (547 miles) and both sides werehappy.

Flying at this low altitude will mark the firsttime Cassini will be below the moon’s ionosphere, a shell of electrons and other charged particles thatmake up the upper part of the atmosphere. As a result, the spacecraft will find itself in a region almostentirely shielded from Saturn’s magnetic field and will be able to detect any magnetic signatureoriginating from within Titan.

Titan orbits within the confines of the magnetic bubble aroundSaturn and is permanently exposed to the planet’s magnetic disturbances. Previous measurements by NASA’sVoyager spacecraft and Cassini at altitudes above 950 kilometers (590 miles) have shown that Titan doesnot possess an appreciable magnetic field capable of counterbalancing Saturn’s. However, this does notimply that Titan’s field is zero. We’d like to know what the internal field might be, no matter howsmall.

The internal structure of Titan can be probed remotely from its gravitational field or itsmagnetic properties. Planets with a magnetic field — like Titan’s parent Saturn or our Earth — arebelieved to generate their global-scale magnetic fields from a mechanism called a dynamo. Dynamo magneticfields are generated from currents in a molten core where charge-conducting materials such as metals areflowing around each other and also undergoing other stresses because of the planet’s rotation.

Wemight not find a magnetic field at all. A positive detection of an internal magnetic field from Titancould imply one of the following:

a) Titan’s interior still bears enough energy to sustain adynamo.b) Titan’s interior is “cold” (and therefore has no dynamo), but its crust is magnetized in asimilar way as Mars’ crust. If this is the case, we should find out how this magnetization tookplace.c) Something under the surface of Titan got charged temporarily by Saturn’s magnetic fieldbefore this Cassini flyby. While I said earlier that the ionosphere shields the Titan atmosphere fromSaturn’s magnetic bubble, the ionosphere is only an active shield when the moon is exposed to sunlight.During part of its orbit around the planet, Titan is in the dark and magnetic field lines from Saturn canreach the Titan surface. A temporary magnetic field can be created if there is a conducting layer, likean ocean, on or below the moon’s crust.

Once Cassini leaves Titan, the spacecraft will perform aseries of rolls to fine-calibrate its magnetometer in order to assess T70 measurements with the highestprecision. We’re looking forward to poring through the data coming down, especially after all thenegotiations we had to make for them!

César Bertucci, a space physicist working at the Instituto de Astronomía y Física del Espacio inBuenos Aires, Argentina, is a Titan expert on the Cassini magnetometer team. He is also a specialist inthe solar wind interaction with weakly magnetized bodies such as Mars, Venus and comets.

Bonnie J. Buratti, Cassini scientist on the Visual and Infrared Mapping Spectrometer Team

After so many close flybys of Enceladus, we’re starting to feel as if this little moon of Saturn is an old friend. But during the encounter planned for Nov. 2, 2009, we are going to get up-close and personal. Cassini is going to take its deepest dive yet into the plumes spewing out from the moon’s south pole to try to learn more about their composition and density.

The spacecraft is going to approach within about 100 kilometers (62 miles) of the surface. We’ve been closer before (25 kilometers or 15 miles), but we’ve never plunged quite so deeply into the heart of the plume.

To get a better sense of our flyby, watch the animation created by my colleague Brent Buffington. This is the seventh targeted flyby of Enceladus, so we sometimes refer to it as “E7.” The video starts out with our approach to Enceladus, rotating through the various instruments scanning Enceladus for data. Then at around 7:40 a.m. UTC (Coordinated Universal Time), we do our long-anticipated flyby through the plumes. The passage will be quick: traveling at about 8 kilometers per second (about 5 miles per second) – fast enough to go from Los Angeles to New York in less than 9 minutes – we’ll spend only about a minute in the plume.Then, we zoom away from the plumes and Cassini turns on an infrared instrument (red rays in the animation) to take the temperature of the south-pole fissures known as “tiger stripes” where the plumes originate. A few minutes later, Cassini uses an ultraviolet instrument (purple rays in the animation) to measure the plumes against the background of the peach-colored Saturn. The infrared instrument then gets another turn to examine Enceladus. For more details, see the mission description.

The focus of this flyby is to analyze the particles in the plume with instruments that can detect the size, mass, charge, speed and composition. Instead of using its eyes (the cameras), Cassini is going to use its senses of taste and smell. But we’re going to get some pretty good pictures too, including some impressive shots of the plumes from far away.

So far, we have detected water vapor, sodium and organic chemicals such as carbon dioxide in the plumes that spew out from the tiger stripes, but we need more detail. Are there just simple organic molecules, or something more complex? This is the first time we’ve found activity on a moon this small (the width of Arizona, 500 kilometers or 310 miles in diameter). We really want to understand what’s driving the plumes, especially whether there is liquid water underneath the surface. If we can put the pieces together – a liquid ocean under the surface, heat driving the geysers and the organic molecules that are the building blocks of life – Enceladus might turn out to have the conditions that led to the origin of life on an earlier version of Earth.

So if this is all so interesting, why did we wait so long to travel into the plumes? One reason is the plunge is tricky. We wanted to make sure we could do it. We worried that plume particles might damage the spacecraft. We did extensive studies to determine that it was safe at these distances. We also wanted to have the right trajectory so we didn’t use an excessive amount of rocket fuel. We are going very fast through this sparse plume; so to play it safe, we’re using Cassini’s thrusters to keep it stable through this flyby.

We’ll be monitoring the thrusters closely because we don’t want to have to use them on another flyby through the plumes planned for April 28, 2010. In the future flyby, we plan on tracking the spacecraft very closely with the radio instruments on Cassini and on Earth so we can measure how the spacecraft wobbles as it passes near Enceladus. These measurements should tell us more about the interior of the moon, including whether it really does have a liquid subsurface ocean. With the thrusters on, we won’t be able tell if the motion of the spacecraft comes from the gravity of Enceladus or the thrusters. We’d like to know whether we can rely on other kinds of attitude control equipment.

We’re all eager to pore over the results of this flyby. Stay tuned. In the meantime, feast your eyes on this map of the surface of Enceladus that the Cassini imaging team has updated and released today. The tiger stripes are located in the lower middle left and lower middle right of the image.

Bonnie J. Buratti, Cassini scientist on the Visual and Infrared Mapping Spectrometer Team

Phew! We made it through the deepest swoop yet down into the plume of Enceladus, the encounter we call “E7” because it’s the seventh targeted flyby of Enceladus.

But now we have our work cut out for the next few weeks as we pore over the data, painstakingly analyzing every signal to understand the composition of the plume and its structure.

So far, we know the Visual and Infrared Mapping Spectrometer (VIMS) was able to get images and data in a variety of wavelengths of light and saw that the plume extends out to at least 1,000 kilometers (600 miles).

We also have striking images of the moon crowned by its glorious plume, which Cassini captured right before its plunge. The images illustrate well that the spectacular plume spewing from the south polar region is composed of many much smaller jets.The images and VIMS data both show that as the moon becomes less and less illuminated by the sun (similar to when our moon approaches the phase known as “new moon”), the plume gets much brighter. These data will be valuable for understanding the detailed structure of the plume and where it connects to the surface.

We have also learned that the density of the plume appears to be less than half of that predicted. Still, the heart of the plume measured on this flyby was about three times denser than the sparser parts of the plume we flew through previously.

There is more good news. We will be able to do the Enceladus flyby on April 28, 2010, on the spacecraft’s reaction wheels. This means we will be able to perform the Radio Science Subsystem experiment with Cassini’s main antenna to understand the interior of Enceladus under the hot south polar region.

During this experiment, antennas from the Deep Space Network (DSN) on Earth will be tracking the spacecraft to see how much Enceladus tugs on it. By measuring this tug, scientists will be able to answer such questions as: How much is the shape of the moon deformed by tidal forces from Saturn? Is there an unusually dense mass under the south pole? (The higher the mass, the larger the tug?)

We know that heating by tidal forces is what drives the plumes, but we’re not sure exactly how. In addition to a possible liquid subsurface ocean, Enceladus may be harboring a dense mass underneath its surface that helped to start and maintain the moon’s current activity.

Just wanted to share our excitement about the reams of data we’re combing through. Now, back to work!

I’m very happy to report that we’ve just put one more major milestone in this remarkable adventure successfully behind us.

Another bold dip over the south pole of Enceladus and another skillful setup for imaging the moon ‘on the fly’ have brought us another bounty of positively glorious views of one of the most fabulous places in the solar system.

for a map of these locales). And of course, as before, we note that the region of the active tiger stripes is finely-fractured throughout and littered with icy blocks.

Our next flyby of Enceladus, as you may know, is not for another year. The sun will be disappearing from the south pole throughout that time, so that by next year we will have a far dimmer view of a shrinking portion of the south polar terrain. So, take your fill of this fabulous place now, because it will be a very, very long time before you see it like this again.

Just in time for Halloween, Cassini does not disappoint and successfully begins to transmit a bag of “science” goodies home. And just like when I was a kid looking through my bag of candy after a long night of trick or treating . . . tonight will be the same as scientists around the country begin to pour over their treats, or in this case data captured on this, our last flyby this year of Saturn’s icy moon, Enceladus.The excitement and joy is relived all over again each time we fly by.What treats and treasures await?I can’t wait to find out!

Well, here we go again! Close on the heels of the first two exciting and successful targeted Enceladus flybys of the Cassini Equinox Mission, we have another Enceladus encounter this week!

Tomorrow is the third of three Enceladus flybys in a series … first the August flyby (referred to as E4 since it was the 4th targeted flyby of the entire mission), then on October 9 (E5) and on Friday, Oct. 31, we’ll do another flyby (E6). These three flybys comprise kind of a set, since they all have similar geometries: the spacecraft approaches Enceladus on an inclined trajectory over the northern hemisphere, closest approach is at a low latitude (near the equator), and then we pass through the plume over the southern hemisphere. Shortly after closest approach, Enceladus enters eclipse behind Saturn and is in darkness for a couple of hours.

Having three flybys with similar geometry is really nice, because it allows us to perform different science experiments on each flyby, since we can’t do everything all in one flyby. It also lets us look for any temporal changes that could be happening at Enceladus, since it is such a dynamic body. E4 was geared toward remote sensing (especially imaging and CIRS) near closest approach, though the fields-and-particles instruments got good data too. E5 was designed for the fields-and-particles instruments, so that they could directly sense the plume as we flew through it. E6 is again designed primarily for remote sensing-and it has a bit more distant closest-approach altitude (200 kilometers or 120 miles), compared to E4 and E5, which approached Enceladus within 50 kilometers (30 miles) and 25 kilometers (16 miles), respectively.

I’ll tell you about the science activities we’ll be doing during this flyby, and you can follow along by watching the accompanying movie (made as usual with grace and skill by Cassini navigator Brent Buffington). Click here for the movie. (At left, a still from the movie.)

Those of you who have been following along with the blog might be familiar with this flyby geometry, and you may also be familiar with this type of movie. For those of you who may be new to this, I’ll introduce the picture: the three panels show what the Cassini spacecraft is doing at each moment during the flyby. The left panel shows the spacecraft relative to the target body Enceladus, and shows which instrument is “prime” by highlighting the field-of-view of that instrument. The lower right shows the field-of-view of the prime instrument, and the upper right shows the fields-of-view of the remote sensing instruments (the cameras, UVIS, VIMS and CIRS), which are all co-aligned.

The movie starts about 8.5 hours before closest-approach, with a UVIS observation of Enceladus and its environment, performing measurements of neutral gases near the moon. That lasts for about 3.5 hours, and then VIMS is prime and stares at Enceladus to get compositional information as Enceladus gets closer and closer. CIRS then takes over (at 4 hours before closest-approach) and does a series of stares and scans with its FP1 (circular) and FP3 (small rectangular) slits, to get surface temperature measurements. Then VIMS performs a half-hour stare (closer to Enceladus this time). ISS takes over at 40 minutes before closest approach, and the spacecraft executes a large turn to put the cameras in position so that they can see the south polar region just as soon as Cassini gets to that location in the trajectory. Paul Helfenstein on the imaging team designed the “skeet shoot” sequence to image the south pole at the highest resolution possible (8.4 meters per pixel for this flyby)! The skeet shoot sequence starts just about two minutes after closest approach. (Closest approach is at 27 degrees south latitude, 97 degrees west longitude.) The imaging team will be able to study the south polar region to look for evidence of varying levels of geyser activity, by combining images from E6 and E4. The skeet shoot is followed by an eight-panel mosaic. Then ISS hands off to UVIS, to execute its closest, highest-resolution-ever scan of Enceladus to image the south pole and get compositional information on the tiger stripe region, as well as on the environment close to Enceladus (notice how the UVIS slit is long and how it extends past the limb of Enceladus). At 50 minutes after closest-approach, CIRS takes over, just as Enceladus is entering eclipse. Without solar illumination, it’s a perfect opportunity for CIRS to measure the thermal situation at Enceladus’ south pole, to determine what kind of heat is coming from the interior. CIRS executes a series of stares and scans with its different fields-of-view, to make these measurements. By the time CIRS is finished and Enceladus is out of eclipse, it’s about 4 hours after closest approach and Enceladus is getting farther away (it’s now smaller than a NAC). VIMS does another stare, this time of the southern hemisphere, and finally UVIS does a measurement analogous to the first one of the sequence, now of the southern hemisphere.

That was a quick few weeks to catch our collective breaths since Cassini’s daring and successful plunge near Enceladus a few weeks ago. Scientists are still grinning profusely from the treasure trove of data from that stunning close approach, largely interpreting in situ measurements of Enceladus’ perplexing plumes. However, as I mentioned last time, this rendezvous with Saturn’s icy satellite is mostly about imaging. Even though the closest approach distance is about eight times higher than our last flyby, imaging is not performed right at closest approach, anyway, so the pictures promise to be spectacular, as always. I can’t wait to see the fruits of our labors!

As always, I’m privileged to provide a maneuver status report a few days before the flyby. This morning, Cassini dutifully fired its small Reaction Control System (RCS) thrusters for about 191 seconds to nail flybys of not only Enceladus on Halloween but Titan three days later as well. Talk about a scientific doubleheader! The burn this morning went quite well, changing the speed of the spacecraft by about 0.23 meters per second (0.51 mph). We will execute a routine Reaction Wheel Assembly (RWA) bias tomorrow, but then it will be time for engineering to hand off the spacecraft to science.

I can’t think of a better way to ring in Halloween—exploring a ghostly white, mysterious, active moon of Saturn nearly one billion miles from planet Earth. May Enceladus show us no tricks and only provide us scientific treats!

It’s become tempting to think of these barnstorming flybys as routine, and to forget how extraordinary they are. Here we are, on one planet in this amazing solar system, flinging this wonderful machine with exquisite precision between the moons of another planet so far away.

This flyby (as show in the illustration), on orbit 91, doesn’t come quite so close to Enceladus as the last three, so we won’t be penetrating the plume so deeply as we’ve been used to recently. That’s OK, because our focus this time is on remote sensing-we’ll be getting images and spectra of the active south polar region comparable in detail to the gorgeous data we obtained from our August 11th, flyby. Originally the October 31st flyby had been planned for a 2,000 kilometer (1,245-mile) altitude, but we moved it down to its present 200 kilometer (120-mile) altitude so we could get a closer look at the surface. We can’t image the surface from 200 kilometers away- we just can’t rotate the spacecraft fast enough to keep track of Enceladus from that range. Instead, our goal is to lock onto Enceladus as soon as we can after the flyby, when we’ll have another good view of the south polar region. The closer we fly to Enceladus, the more quickly the direction to the moon stabilizes as we recede, and the sooner we can track it. Imagine trying to read a billboard from a speeding car-it’s a lot easier to read (if you’re not driving!) when it’s receding in your rear view mirror than when you’re passing it.

Image above: This diagram shows the trajectory of Cassini’s closest Enceladus flybys from the Prime and Equinox missions, relative to the south polar plume, which is shown in false color based on an image taken by the Cassini cameras in April 2007. Flybys on orbits 3 and 121 do not come quite close enough to Enceladus to appear on this graphic.

Credit: NASA/JPL/SwRI/SSI

Our own instrument, the Composite Infrared Spectrometer (CIRS) will once again be mapping the heat radiation from the warm tiger stripe fractures, trying to understand how hot the fractures are, and exactly where the heat is coming from. We only had time to map a small fraction of the active fractures from close range in August, so this time we’ll be looking at different regions, in cooperation with the imaging camera and the ultraviolet spectrometer which will be observing simultaneously for much of the time.

We’ll be following up on some of our August 11th discoveries. Back then, we got a beautiful spectrum of one of the most active regions of the fracture Damascus Sulcus, allowing us to make some precise temperature measurements. We’re really interested in the temperatures, because the warmer the fractures are on the surface, the more likely it is that liquid water lurks somewhere below. The highest temperatures we saw, 167 Kelvin or -159 Fahrenheit, were a bit lower than we had estimated from our less precise data from the March 12th flyby (at least 180 Kelvin or -136 Fahrenheit), though both numbers are dramatically warmer than we would expect at this time of year if internal heat wasn’t leaking out of Enceladus (roughly 60 Kelvin or -352 Fahrenheit). Whether the Damascus fracture has really cooled since March, or whether our March measurement was an overestimate, or some other factor explains the discrepancy, is one of the things we’re still puzzling over, and maybe this week’s data can help us sort that out.

Another thing we’ll be doing is measuring the total amount of heat energy coming out of the south pole. Knowing the total horsepower of Enceladus’ heat engine is crucial for understanding what’s driving the activity there. We’re pretty sure the deformation of Enceladus by Saturn’s tides is the ultimate power source, but so far none of the theorists have been able to explain in detail how that source can continuously supply the roughly 6 Gigawatts of power that CIRS is seeing. So we’ll be trying to refine that power estimate on this flyby. Whether the new observations will make life easier or more difficult for the theorists’ remains to be seen!

Hi everyone, Just got back from the DPS science meeting in Ithaca, NY (where lots of great Enceladus results from previous flybys were presented!). It was a busy week but I got a chance to have a quick look at the new UVIS data from last week’s flyby. It looks good!!

Looks like we got some really good-quality data, and we’ll be able to say something about surface composition at the south pole, and potentially about variations in surface composition, as well as about the environment around Enceladus. I need to dig much deeper into the data though, before I say anything more!

Wow. I have to say, even though it’s pretty hectic to analyze new data while going to meetings and giving talks and writing papers (all at once)– and all the while preparing for the next flyby (Oct.31!) –it is so useful to have multiple flybys of Enceladus. Enceladus is such a crazy and dynamic object, that it is incredibly vital to get multiple observations and flybys to be able to really find out what’s going on. Hearing some of the DPS talks on Enceladus made me feel like we’re just starting to get enough data to begin looking at trends and really get to know Enceladus. So it’s really getting exciting. So even though this flyby went very smoothly, we can’t get all the data we need to understand Enceladus on just one flyby! This is partly because Cassini is a complicated spacecraft and not all instruments can get data optimally at once, but also because Enceladus is so interesting and puzzling that many flybys are required to start to understand it.